Process for producing aliphatic esters



April 3, 1956 M. MENTION ET AL 2,740,800

PROCESS FOR PRODUCING ALIPHATIC ESTERS Filed May 18, 1953 SceuasuvaCOLUMN Human Sum-we:

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United States Patent 2,740,800 PROCESS FOR PRODUCING ALIPHATIC ESTERSMaurice Mention and Pierre Gotlet, Melle, Deng-Sevres, France, assignorsto Les Usines de Melle (Societe Anonyme), Saint-Leger-les-Melle, France,a corporation of France 1 Application May 18, 1953, Serial No. 355,724Claims priority, application France December 5, 1952 6 Claims. (Cl.260-4103) This invention relates to a process for making aliphaticesters, particularly by reaction of propylene with acetic or otheraliphaitc acid in the presence of a strong mineral acid.

It is known that acetic acid can react with propylene in the presence ofsulfuric acid. Many modes of carrying out such reaction have beendescribed, to produce a mixture comprising sulfuric acid, mono-isopropylsulfate, acetic acid and isopropyl acetate, but containing in additionpropylene polymers and decomposition products.

Such processes have been carried out in batches, each batch (containinga mixture of acetic and sulfuric acids) being treated with propyleneuntil the latter is no longer absorbed.

The reaction mixture obtained is then treated for recovery therefrom ofthe ester formed, the treatment generally consisting in diluting themixture with water to isolate a mixture of acid, ester and water bydecantetion and/or distillation, the acid-ester-water mixture being thenseparated into its components by known means. The recovered sulfuricacid, thus, is in dilute form-"and must be concentrated before reuse. i

A process of the batch type has: been proposed which involves theproduction of the ester in'a reactor, removal of the reacted mixture anddistillation of same by bubbling an olefine therethrough to removesome'of the' ester. Thereafter the remainder of the mixture-is re turnedto the reactor for further processing.

The principal object of the present invention accordingly is to producea simple and efiicient process for the production of aliphatic esterswhich shall overcome in part at least some of the disadvantages of theprior processes.

The invention accordingly comprises the novel processes and steps ofprocesses, specific embodiments of' which are described hereinafter byway of example and in accordance with which we now prefer to practicethe invention.

We have found in accordance with our invention that such isopropylesters can be produced by continuously.

feeding propylene and saturated aliphatic acid having 2-8 carbon atomsinto a bath maintained at about 60-80 C. The corresponding isopropylester is thereby produced. The bath at the equilibrium has approximatelythe following composition:

Percent Sulfuric acid 20-30 Aliphatic acid 5-30 isopropyl ester 5-10Water 0.5- isopropyl hydrogen sulfate 69.5-20

be circulated back to the system. Under such conditions 2,740,800Patented Apr. 3, 1956 "ice Percent Sulfuric acid 20-30 Acetic acid 5-30isopropyl acetate 5-10 Water 05-10 the remainder being isopropylhydrogen sulfate. bath may be initially formed by any suitable means. Inoperation, the bath is fed with acetic acid and propylene underconditions hereinbelow set forth.

TEMPERATURE The working temperature is maintained substantially constantat a value in the range 60-80 C. The preferred temperature is between 65and 70 C. because at such temperatures polymer formation is very lowwhile the bath is still capable of absorbing enough pro-.

pylene. As a matter of fact, the absorption capacity per hour of thebath increases as temperature increases but polymer formation alsoincreases as temperature increases.

ACETIC ACID FEED Acetic acid is continuously fed to the bath at a ratesuch that the acetic acidity in the bath remains substantially constantat the chosen value. acetic acidity is in the range of 5-30%. However,the preferred range is 10-20% because below 10% the quickness ofabsorption of propylene is relatively low, whereas above 20% more aceticacid is carried 01f by the nonabsorbed propylene, and, as a result,recovery of isopropyl acetate in a pure state is more costly.

PROPYLENE FEED For maintaining in equilibrium the composition of thebath and removing the isopropyl acetate as it is formed, it is necessarythat the gaseous feed rate be maintained between certain limits. Thepropylene feed rate to the bath should be of 2-5 cubic meters per hourper kg. of bath, preferably 2.5-4 cubic meters per hour per kg. of bath.Under such conditions the Whole of the isopropyl acetate formed iscarried off as Vapors by the excess gas, together with a quantity ofacetic acid and small amounts of isopropyl alcohol and isopropyl oxide.

The resulting gaseous mixture is freed from the vapors it contains,preferably by cooling then, if need be, washing with'acetic acid oranother liquid capable of dissolving isopropylacetate but from whichisopropyl acetate can be readily separated, for example throughdistillation. The gas freed from the products carried 0a is recycled tothe reaction bath.

RiCHNESS OF THE GAS IN THE CYCLE We may use either pure propylene or agaseous mixture containing high proportions .of propylene. together withother gases which do not react with sulfuric acid or acetic acid, such,for example, ,as propane, ethane, methane, air, nitrogen, butane, etc.Where such propylene-containing mixtures are fed to the cycle, it isnecessary continuously to discard from said cycle an amount'of gascorresponding to the amount of non- As stated above, the

absorbable gases introduced. Of course, it is not possible to discardonly the non-absorbable gases, so that the discard always contains anamount of propylene. The discarding is controlled so as to maintainsufficient richness of propylene in the cycle. The propylene richnessmay be as low as 30% of propylene by volume but in order that theabsorption capacity per hour of the bath be high, it is recommended tomaintain said richness above 50% by volume, for example between 50% and90% by volume.

The process of this invention may be carried out in the apparatusdiagrammatically shown in the attached drawing, forming part of thisapplication. in this drawing, 1 is the reaction vessel or reactor whichpreferably is a tower into the bottom part of which propylene isintroduced through a porous plate 2 or any other means for distributinga gas throughout a liquid. The required temperature is obtained andmaintained by means of a heating device 3 which may be a steam jacket,an electrical winding or any other conventional device. Aliphatic acidsuch as acetic acid from tank 4 is fed to reactor 1 through pipe 5fitted with a control valve 6. Sulfuric acid is fed through pipe 1A. Themixture of gases and vapors leaving reactor 1 through pipe 7 areintroduced into a condenser 8, then, if need be, into a scrubbing column9 to wash them. Column 9 is fed at its upper part with a suitablewashing liquid, more particularly aliphatic acid from tank 4, fedthrough pipe 10 fitted with a control valve 11. The gases leaving fromthe top of column 9 are recycled to reactor 1 through pump 12. Residualmixture of propylene and inert gas if any is discarded through pipe 13.Fresh propylene or proplyene-containing gas is fed through pipe 14.Regulation of the throughput is effected by means of valve inserted inpipe 13. the bath may be effected through a pipe 16 which, for the sakeof illustration, has been placed at the bottom of reactor 1 in thedrawing.

Column 9 may be removed from the apparatus if either condenser 8 iscooled very strongly so that the ester content of the escaping gases isvery low, or the non-condensed ester is allow to remain the gas recyclebut such a feature results in diminution of production capacity of thebath.

The liquid from condenser 8 and that from column 9 when such column isemployed are collected and treated by conventional distillationprocesses for separating isopropyl ester therefrom. Recovered aliphaticacid is sent back to tank 4 while isopropyl alcohol and isopropyl oxidewhich are formed in small amounts may be sent back to the bath wherethey are converted into isopropyl ester. It is thus possible to produceonly isopropyl ester without any by-product.

From the above disclosure it should be understood that an importantcharacteristic of our invention consists in the continuous removal fromthe bath of the isopropyl ester as it is formed therein. This is done bythe propylene containing gas of which only a part reacts while theremainder carries off the ester. This feature makes it possible tooperate at a temperature substantially below the boiling point of thereaction mixture and to perform the production and separation of theester in a one-phase, continuous process.

The following examples will show how our invention may be carried intoeffect. In these examples propylene and the aliphatic acid are fed intoa bath whose equilibrium composition is given. This bath was prepared asfollows for Example 1:

Sulfuric acid, water and isopropyl alcohol were introduced intoreactor 1. There was then fed into this mixture propylene and aceticacid, same being reacted, so that the contents of isopropyl acetate,isopropyl hydrogen sulfate, acetic acid, sulfuric acid and water reachedthe equilibrium composition of the hath given in Example 1 below and thebath content was maintained at such Discarding of a proportion of tcomposition. The baths in the other examples were similarly prepared.

Example 1 Composition of the bath: Sulfuric acid, 3.2 kg. Acetic acid,5.2 kg. Isopropyl acetate, 1.3 kg. Water, 1 kg. Isopropyl hydrogensulfate, 9.3 kg. Feed:

16 kg. per hour of 99% acetic acid (of which 7.4

kg. per hour are recycled), and 3.85 cubic meters per hour of 99.4% (byvol.)

propylene (through pipe 14). Volume of discarded 93% propylene (pipe13): 0.33

cubic meter per hour. The remainder of the gas is propane. Temperatureof the bath: C. Feed rate to bath of the propylene gas: 85 cubic metersper hour. Pure isopropyl acetate produced: 14.6 kg. per hour. Thus theyield is substantially 100%.

Example 2 Composition of the bath: Sulfuric acid, 4.6 kg. Acetic acid,1.6 kg. Isopropyl acetate, 1.1 kg. Water, 1.75 kg. Isopropyl hydrogensulfate, 7.7 kg. Feed:

14 kg. per hour of 99.6% acetic acid (of which 8.6

kg. per hour are recycled), and 2.2 cubic meters per hour of 99%propylene (pipe 14). Volume of discarded 56% propylene (pipe 13): 0.053

cubic meter per hour. The remainder of the gas is nitrogen. Temperatureof the bath: C. Feed rate to bath of the gas: 55 cubic meters per hour.Pure isopropyl acetate produced: 9.2 kg. per hour. Thus the yield issubstantially 100%.

Our invention is particularly suitable for producing isopropyl acetatebut is not limited to such production. In accordance with our inventionwe may react propylene with aliphatic acids other than acetic, such forexample as propionic, butyric and isobutyric acids and the homologues ofsuch acids having 5 to 8 carbon atoms. Formic acid, however, cannot beemployed. The conditions of sulfuric acidity, amount of aliphatic acid,temperature, rate of passage of gas, should be adjusted according to thealiphatic acid in use, but should be kept within the limits hereinaboveset forth.

Example 3 Composition of the bath:

Sulfuric acid, 3.95 kg. Butyric acid, 2.84 kg. Isopropyl butyrate, 0.90kg. Water, 0.70 kg. Isopropyl hydrogen sulfate, 8.65 kg. Feed: 7.5 kg.per hour of pure butyric acid (of which 0.9 kg. per hour are recycled),and L8 cubic meters per hour of 99.4% propylene (pipe 14). Volume ofdiscarded 46% propylene (pipe 13): 0.02

cubic meter per hour. The remainder of the gas is ethylene, which is notabsorbed under the conditions described. Temperature of the bath: C.Feed rate to bath of the gas: 60 cubic meters per hour. Pure isopropylbutyrate produced: 9.75 kg. per hour. Thus the yield is substantiallyExample 4 Composition of the bath:

Sulfuric acid, 2.96 kg. Butyric acid, 2.25 kg. Isopropyl butyrate, 1.12kg. Water, 095 kg. Isopropyl hydrogen sulfate, 9.70 kg. Feed: 11 kg. perhour of pure butyric acid (of which 3.2 kg. per hour are recycled), and2.25 cubic meters per hour of 99.8% propylene (pipe 14) Volume ofdiscarded 93% propylene (pipe 13): 0.064

cubic meter per hour. The remainder of the gas is propane. Temperatureof the bath: 70 C. Feed rate to bath of the gas: 70 cubic meters perhour. Pure isopropyl butyrate produced: 11.5 kg. per hour. Thus theyield is 99.8%.

Example Composition of the bath:

Sulfuric acid, 3.15 kg. Octanoic acid, 1.10 kg. Isopropyl octanoate,0.80 kg. Water, 0.95 kg. Isopropyl hydrogen sulfate, 9.75 kg. Feed: 3.06kg. per hour of 98% octanoic acid (of which 0.06 kg. per hour arerecycled), and 0.713 cubic meter per hour of 95% propylene (pipe 14)Volume of discarded 84% propylene (pipe 13) 0.223

cubic meter per hour. The remainder of the gas is propane. Temperatureof the bath: 77 C. Feed rate to bath of the gas: 75 cubic meters perhour. Pure isopropyl octanoate produced: 3.8 kg. per hour. Thus theyield is substantially 100% The weight of sulfuric acid in each of theabove examples is given as H2504.

What we claim is: Y

1. A process which comprises continuously feeding acetic acid andpropylene into a bath of approximately the following composition:

maintaining said bath at a temperature of about 60-80 C., the rate offeed of said propylene being about 2-5 cubic meters per hour ofpropylene per kg. of said bath, the rate of feed of said acetic acidbeing suflicient to maintain the bath content thereof within theabove-mentioned percentage range, and removing isopropyl acetate fromthe bath by gas containing propylene at substantially the rate at whichthe isopropyl aceate is formed in the bath.

2. A process in accordance with claim 1 above, in which the gas andvapors leaving the bath are cooled to condense vaporous constituents andthe condensate is treated for recovery of isopropyl acetate therefrom.

3. A process in accordance with claim 2 above, in

Percent by weight Sulfuric acid -30 Aliphatic acid 5-30 Isopropyl ester5-10 -Water 0.5-10

lsopropyl hydrogen sulfate 695-20 the rate of feed of said aliphaticacid being sufficient to maintain the aliphatic acid content of the bathwithin the range mentioned above, the rate of feed of propylene beingabout 2-5 cubic meters per hour per kg. of said bath, and removing theisopropyl ester from the bath by gas containing propylene atsubstantially the rate at which the isopropyl ester is formed in thebath.

5. A process which comprises continuously feeding butyric acid andpropylene into a bath of approximately the following composition:

Percent by weight Sulfuric acid 20-30 Butyric acid 5-30 Isopropylbutyrate 5-10 Water 0.5-10 Isopropyl hydrogen sulfate 69.5-20

Percent by weight Sulfuric acid 20-30 Octanoic acid 5-30 Isopropyloctannate 5-10 Water 0.5-10 Isopropyl hydrogen sulfate 69.520

maintaining said bath at a temperature of about C., the rate of feed ofsaid propylene being about 2-5 cubic meters per hour of propylene perkg. of said bath, the rate of feed of said octanoic acid beingsuflicient to maintain the bath content thereof within theabovementioned percentage range, and removing isopropyl octanoate fromthe bath by gas containing propylene at substantially the rate at whichthe isopropyl octanoate is formed in the bath.

References Cited in the file of this patent UNITED STATES PATENTS2,079,652 Davis et a1 May 11, 1937

4. A PROCESS WHICH COMPRISES CONTINUOUSLY FEEDING PROPYLENE AND ASATURATED ALIPHATIC ACID HAVING 2 TO 8 CARBON ATOMS INTO A BATHMAINTAINED AT ABOUT 60-80*